1. Technical Field
This invention relates generally to battery charging devices, and more particularly to multiple battery charging devices for electronic devices.
2. Background Art
Portable computers, personal digital assistants (PDA""s), cellular telephones, pagers, calculators, and other such electronic devices are commonplace in today""s mobile society. One of the reasons these electronic devices are so popular is that they are portable, i.e. they provide a user with virtual freedom regarding the location of their use. Although these devices may be powered by plugging them into a standard AC outlet, AC power is often not convenient or accessible. Hence, batteries, by offering a portable source of power, provide portability and added utility to these electronic devices.
Although battery technology has progressed greatly in recent decades, a single battery is sometimes unable to meet a user""s demands. For example, many cellular telephone service providers are offering plans with 3000 plus minutes of talk time or more per month. Some business people talk on their cellular phones six or more hours per day. Typical cellular telephone batteries provide only three to four hours of talk time before needing to be recharged. Consequently, some users carry two or more batteries with them so that a spare is ready when the first battery dies. To remain on the go, users now demand shorter charge times in addition to extended battery life. They also want to be able to quickly charge two or more batteries at the same time.
One solution to the problem of how to quickly recharge two or more batteries is to charge the batteries serially. In other words, when the two batteries are placed in the same charger, the charger completely charges the first battery. The charger then switches to the second battery and charges it. Total charging time is the charging time of one cell multiplied by the number of cells. Another solution to the problem with quickly recharging multiple batteries was to charge each battery in a charging system with its own power line or charging system.
Both prior art solutions, however, present problems. A problem with the first solution is that it is not efficient, in that it takes quite a long time to fully charge both batteries. The second solution is prohibitive in terms of both cost and the amount of space required for multiple charging circuits. For these reasons, there is a need for an adaptive multiple battery charging apparatus that allows simultaneous charging of multiple batteries with a single battery charging system.